1. Field of the Invention
The invention relates to a microscopy system and a microscopy method which may be in particular used for observing an emission of fluorescent light at wavelengths of the near infrared and/or infrared. Further the invention relates to a method of treating an aneurysm.
Fluorescent substances and fluorescent dyes showing a fluorescence at wavelengths in a region of the near infrared or infrared are used in medical applications for various purposes such as visualizing particular types of tissue, tissue structures and tissue functions. Herein, a fluorescent substance or dye or a precursor of such fluorescent substance or dye is applied to a patient under examination. The dye accumulates in particular types of tissue and tissue structures, and by observation of the fluorescent light such types of tissue and tissue structures, respectively, may be visualized and identified by an observer. Optical tools are used to visualize the some times weak intensities of fluorescent light.
2. Brief Description of Related Art
One example of a suitable fluorescent substance is indocyanine green (ICG). From the article by T. Kuroiwa et al., “Development and Clinical Application of Near-Infrared Surgical Microscope Preliminary Report”, Minim Invas Neurosurg 2001; 44: 240-242, there is known a method and system for observing the fluorescence of this substance. An excitation wavelength of the fluorescence of the substance is about 780 nm, and a fluorescent emission wavelength is about 835 nm. For an observation of a tissue in which ICG has accumulated by a microscope, the tissue is illuminated with light of a main wavelength of 800 nm of a laser light source or of a halogen lamp. In a beam path of the illuminating light there is positioned a band-pass filter which allows only light having wavelengths between 760 nm and 810 nm which is light for exciting the fluorescence to pass there-through. The tissue is imaged onto a camera by a microscopy optics wherein a further band-pass filter allowing only light having wavelengths between 820 nm and 920 nm which is fluorescent emission light of ICG to pass there-through. An observation of images detected by the camera allows to identify those regions of the tissue in which the fluorescent substance has accumulated. It is, however, not possible to perceive surrounding regions of this tissue. Such surrounding regions would emit visible light under a suitable illumination. However, such illumination with visible light is not possible since the laser light source does not provide such light, and the band-pass filter in the beam path of the light source blocks such visible light from incidence on the tissue. A surgeon performing a surgical treatment of the tissue region has to illuminate the tissue region with visible light for perceiving an optical image of the tissue region with visible light in a first step, and he has to observe the fluorescent image thereafter for perceiving the fluorescent light in a subsequent second step. Further, an illuminating light beam of the laser light source and an illuminating beam for illuminating the tissue region with visible light are incident on the surface region under different angles such that both light beams generate different types of shadows on the tissue region. Such different shadows render it more difficult to correctly associate regions of the fluorescent image with regions of the visible image of the tissue region.
Such procedure is complicated and requires a high power of concentration of the observer since he must remember the image previously perceived at the respective different type of illumination.
The article of T. Kuroiwa et al., discloses an application of the ICG fluorescence for obtaining information about deep-seated tissues. The excitation and emission wavelengths of ICG lie within the “optical window” of tissue, where absorption attributable to endogenous chromophoreous is low. Near infrared light can therefore penetrate tissue to a depth of several millimeters to a few centimeters. According to the article, a near infrared fluorescence of vessels on the brain surface was observed through the dura mater. The article concludes that a stronger fluorescence emitted from the ICG will be necessary for the application to have practical use even for imaging venous vessels.
A cerebral or intra-cranial aneurysm is a dilatation of an artery in the brain that results from a weakening of the inner muscular layer of a blood vessel wall. The vessel develops a “blister-like” dilation that can become thin and rupture without warning.
The vascular dilation itself is referred to as an aneurysm sac, and an entrance area that leads from the parent artery to the aneurysm sac is referred to as aneurysm neck. According to a conventional surgical technique of medical therapy of the aneurysm, a clip is used to close the aneurysm sac. Thereafter, the surgeon has to verify that the aneurysm sac is completely closed and that a sufficient vascular flow is guaranteed in the parent artery and surrounding vessels.
According to a conventional technique the vascular flow is assessed by x-ray angiographie. For performing x-ray angiography, the surgical microscope which must be used for performing the surgery and positioning the clip has to be dismounted first, the x-ray apparatus has to be mounted thereafter, and the surgeon has to leave the room while the x-ray images are recorded. Development and interpretation of the x-ray image will take some ten minutes. Intra-operative x-ray angiography is often not used in practice for blood flow assessment due to the long duration until interpretation of the results. Further, an imaging resolution achievable with x-ray angiography is not sufficient for assessing blood flow in small vessels. Further, a complication rate associated with x-ray angiography is considered to be relatively high due to the necessity of applying a corresponding contrast agent via a catheter into an artery of the patient.